The present invention relates to a single-sided cutting insert preferably for turning which consists of a wafer having a polygonal basic shape, preferably a triangular basic shape. The cutting insert comprises an upper face, a lower face and a plurality of side surfaces joining said faces. The faces are parallel. The side surfaces join each other at corners. Cutting edges are formed along lines at the upper part of said corner. The cutting edges are joined in cutting tips having a mutual plane. The lower face is provided only to abut a base surface of a cutting insert site. Each lower part of the corners comprises a projection connected to two side surfaces.
Hitherto known cutting inserts for turning are abutting the cutting insert site of the tool shank with planar lower faces. The drawback with this type of abutment is the wobble-tendencies that arise due to difficulties in forming completely planar contact surfaces. Thus the cutting insert risks riding upon a point in the middle of the base surface. Furthermore these surfaces can easily be contaminated such that the cutting insert will be caused further instability, which negatively influences the result of the machining.
The object of the present invention is to design the lower face of a cutting insert such that the above-mentioned and other problems are solved .